Screw



April 6, 1937. E, PAYNE 2,076,041

SCREW Filed NOV. 29, 1955 @Qyi. 7

i ll

Patented Apr. 1 937 SCREW Ernest I ayne, Chicago, lll., assignor to Central Screw Company, Chicago, 111., a corporation of Illinois Application November 29, 1935, Serial No. 52,152

' 3 Claims.

This invention relates to screws and particularly to that class of screws generally'referred to as self-tapping. Some self-tapping screws cut the female thread and others extrude the metal to form the female thread and it is this latter type of self-tapping screw to which this invention is more particularly related.

Self-tapping screws are extensively used in industries requiring high speed production meth- 1Q ods, such as the radio industry, for example. In building the frame for a radio chassis a number of holes are punched some of which will be used in building one particular model such as a five tube radio, and some of these holes and others will be used in-building a six tube radio and some of these holes and still others will be used in building a seven tube radio, and so on. It would be wasteful to thread all of the holes for ordinary screws because many times only some of the holes are used. Hence, it is desirable to threadonly those holes needed for the particular model to be constructed and this can best be done by the use of self-tapping screws. The end of the shank of all self-tapping screws is tapered so that it may be inserted in the hole which has a diameter equal to or but slightly greater than the root diameter of the screw. An automatic socket wrench is then applied to the head of the screw to drive the screw in place. The socket of the wrench is generally rotating when it is applied to the stationary screw head and quite often the screw head is damaged or broken by the violent engagement of the socket with the screw head.

It is an important object of the invention to provide ahead on a self-tapping screw that will center itself in the socket of a socket wrench without damaging or breaking the screw head.

Another object is to insure even pressure of the socket wrench on all sides of the screw head in I 4 driving a self-tapping screw so that the sore will not skew while being driven.

The metal extruded during the formation of the female threads extends from the surface of the plate in which the threads are formed and the extruded metal has prevented the heads of screws used heretofore from seating flush with the surface of the plate, and it isa further object of the invention to provide a screw head which will receive the extruded metal and set flush with the surface of the plate so that there will be no gap between the head and plate surface.

In some instances the head of the screw is first inserted in the socket of a socket wrench and then the operator by use of the wrench inserts 65 the tapered end of the screw in the hole and operates the wrench to drive the screw. The length of the screw is sometimes less than the depth of the socket and in such case the screw becomes lost therein and it is impossible to insert 60 the tapered end of the screw in the hole. It'is a still further object of the invention to prevent the screw from becoming lost in the socket.

The end of the socket wrench has engaged the material into which the screw was being driven and has marred the surface of the material about the screw head and it is a still further object to prevent the driving tool from marring the surface of the material about the head.

Referring to the drawing wherein I have illustrated a selected embodiment of the invention Fig. 1 is a side elevation partly broken away showing the screw in use to hold two plates together; Y

Fig. 2 is a side elevation showing the screw about to be threaded into an opening provided therefor in plates to be held together by the screw;

Fig. 3 is a top plan view of the screw;

Fig. 4 is a perspective view; and

Fig. 5 is a bottom plan view.

The screw consists of a shank 6 and a head I. The shank is preferably threaded with a standard thread and is tapered at the free end 8 thereof with the first few threads of the shank located on the tapered end. The shank is preferably case hardened so that the threads on the shank cannot be easily deformed and so that they will be capable of forming threads in the female member. The head has a shoulder 9 extending outwardly of the head around the periphery thereof and located at the bottom face of the head where the head joins the shank. The top of the head is substantially rounded at Ill and has the general shape of a spherical segment. A plurality of flat side faces H are provided on the screw head and which lie in vertical planes. The head illustrated is hexagonal but my invention also contemplates the use of a tetragonal head or a head having any desired number of sides. The top mergesinto the fiat side faces without a sharp angle at the juncture .between the top and side faces. A slot l2 map be provided across the center of the rounded top on the head to receive an ordinary screw driver. An annular recess I3 is provided in the underside of the head adjacent the juncture of the head with the shank.

A plate ll of sheet material and a plate l5 also of sheet material are shown in the drawing to illustrate the manner in which the screw secures the plates together. The plate It is provided with an opening I6 of a larger diameter than the outside diameter of the threaded shank of the screw and plate It is provided with an opening I! of a diameter less than the outside diameter of upon the nature and thickness of the material, upon the diameter of the screw and upon the size of the thread, it may be desirableto use an opening either larger or smaller than an opening 5 slightly greater than theroot diameter of the screw. In using the screw the tapered end thereof is first inserted in theopenings provided in the plates, Fig. 2. and then'the socket of an automatic socket wrench is engaged with the head of the screw to drive the screw into the opening ll, Fig. 1. In engaging the revolving socket wrench with my screw head the rounded top-thereof .serves as a guide .to guide the socket over the head and into engagement with the side faces whereupon the socket will turn thehead and shank to drive the screw home. On screws heretofore provided the sides of the socket engage the flat or substantially flat top of the screw head andgreat difllculty is encountered in registering the socket with the side faces and while trying to register it the revolving socket often chips or breaks the head. The end of the socket engages the shoulder 9 and presses equally all around the head so thatthe screw is driven straight into the opening 'l'l. Heretofore the necessary clearance between the socket and side faces of the screw head permitted the screw to skew in driving it home and this is avoided in my screw because so the pressure on the shoulder 8 is distributed equally throughout the extent of the shoulder and the shoulder also will space the end of the driving tool from the surface of the material to 3 prevent marring the surface.

of the socket wrench before inserting'the screw in the opening II in the plate It the shoulder 8 acts as a stop to prevent the screw from going too far in the socket and becoming lost therein.

When the screw is driven into the plate it the metal about the opening ll will be extruded asillustrated in Fig. l, and the extruded metal extends from-thesurface of the plate I! through the opening it in the plate It and into the recess 45 Bin the bottom side of the head. .Heretofore self-tapping screws have been made with the bottom side of the headjflat and the extruded metal has held the head from flush engagement with the surface of the plate I4 and by providing 50 the recess II in my head I accommodate the extruded metal and permit the head to become flush with the plate It. and firmly engage therewith. An additional advantage is derived from having the screw head "firmly engage the surface 55 of plate It in that there is friction developed therebetween which reduces the liability of the screw from becoming unintentionally loosened by vibration or the like. The shoulder 8 increases the normal area of contact between the head and so the plate It and this increased contact enhances the frictional engagement of the head and plate. After the device in which my screw is used leaves the place of manufacture and goes into the hands of a consumer it is often necessaryto c5 repair the device and in making repairs .thereto it is often necessary to remove the screws and frequently the repairman does not have in his equipment a socket wrench to use for this pur-' pose. Also the screws are often in a location in- 70 accessible to an ordinary open end wrenchor the like and I have, therefore, provided the slot I2 so that the screw may be readily removed with when the screw heads are placed in the socket I an ordinary screw driver and after the repairs have been made the screw may be replaced with the same instrument. I prefer to use a standard thread on my screw so that if a replacement of the screw is necessary when in the hands of the consumer it may be replaced with an ordinary standard screw.

The invention may be adapted for devices of many diiferent forms and for many diflerent purposes and I do not limit it to the forms herein shown and described but reserve the right to use it in any form and for any purpose forlwhich it is or may be adapted within the scope of the following claims.

I claim:

1. Aself-tapping screw adapted to secure two pieces of material together andcomprising a solid head and a shank joined together'and capable of extruding-material in forming female threads in the material to be held by the screw, said head having a bottom face and an annular recess therein at the juncture of the head and shank to receive the extruded material and enable the bottom face of the head to firmly engage the surface of the material to be held by the screw, said head being adapted to be embraced by the socket of a driving tool, and a peripheral shoulder on the head extending outwardly therefrom at the bottom face and engageable withthe' free edge of the socket of the driving tool to prevent the screw from becoming lost in the socket of the driving tool. to insure straight-driving of the screw by a driving tool and to increase the seating surface of the bottom face in engagement with the surface of the material to be held by the screw and to space the end of the driving tool from the surface of the material.

2. A self-tapping screw adapted to secure two pieces of material together and comprising a solid head'and a shank joined together and capable of extruding material in forming female threads in the materialto be held by the screw. a bottom face on said head providing an extended seating surface adapted to tightly engage the adjacent surface of the material to be secured and to cooperate with the threads of the screw to hold said two pieces of material together, and aplurality of vertical side faces on said head adapted to be embracedby and held in the socket of a driving tool, said head having a recess extending thereinto at the juncture of the bottom face and shank to receive the extruded material. the depth of said recess being less than the-height of the side faces from the bottom face.

3. A self-tapping screw adapted to secure two pieces of material together and comprising a head and a shank joined together and capable of extruding material and forming female threads in the material to be held by the screw, and a bottom face on said head providing an extended seating surface adapted to tightly engage the adjacent surface of the material to be secured and to cooperate'with the threads of the screw to hold said two pieces of material together, said head having an annular recess extending into. the bottom face thereof at the juncture ofthe bottom face and shank to receive the extruded material. and said head being solid from side to side thereof above said recess and the portion of the head between the recess and the outside of said head being rigid and unyielding.

ERNEST PAYNE. 

